Maia 300 networking insights: 1. The NIC is on the die and built only for scale-up: low latency, high bandwidth between accelerators. 2. Tier 1 is copper inside the rack. Neighboring Maias talk the most (tensor parallelism), so about half of each chip's bandwidth stays in the server and half goes to the in-rack switch. 96 accelerators per rack. 3. Tier 2 is optics between racks, and it's still scale-up. Up to 128 racks, 12,288 accelerators, one domain, one communication stack. 4. Standard Ethernet switches and cables for the scale economics, with Microsoft's own transport on top. The NIC and transport are where Microsoft does its own engineering. 5. Why go past one rack? Bigger models, more aggressive sharding, and flexible job placement. The scheduler can put a job anywhere in 12,288 chips. 6. Fast data movement. Prefill and decode run as separate pools, and the KV cache moves between them over the scale-up fabric, never the slower scale-out network. For agents with long context, that's the expensive data movement.